Multiple collet holders, or fixtures constituting a machining center, are already known in the art. For instance, U.S. Pat. Nos. 3,632,112 and 4,103,589 show multiple collet or spindle chucks or heads. These units present a plurality of work-pieces to a machining tool, and they also utilize hydraulic pressure for clamping the tool in a collet. That is, the hydraulic pressure is applied to axially move the collet, in the usual manner, so that the collet will clamp onto the work-piece.
However, the prior art does not disclose a multiple collet holder wherein each collet is individually held against rotation, so that the machine can be firm and accurate, nor does the prior art disclose the arrangement for individually actuating each collet for clamping and releasing a work-piece. That is, the prior art is aware of only collet holders wherein the collets can rotate and/or the multiple collets are clamped in unison, rather than individually. Still further, the prior art is incapable of having the collet receive the work-piece from either axial end of the collet, and having the work-piece extend beyond the collet.
Further, the present invention improves upon the prior art in that it provides a multiple collet holder wherein the collets can be individually clamped, and the collets are specifically retained against rotation for optimum machining procedures. Additionally, the work-pieces held by the collets of the present invention can be inserted from either end of the collet and can protrude from either end of the collet, and thus long work-pieces can be accomodated by the present invention. Also, the present invention is not susceptible to impairment by dirt, oil, metal chips, and the like which are commonly prevalent in machining.